Studies on the formation of a permeable cell membrane junction

Summary

Coupling by permeable membrane junction between single pairs of newt embryo cells (macroblastomeres) was inducedin vitro. At the same time, the resistance of the developing cell-to-cell diffusion channels (junctional membrane) and that of their insulation from the exterior (junctional insulation) were determined by electrical measurement. From the moment the cell coupling was first detected electrically, the resistance of junctional membrane fell gradually to a relatively steady level during 0.5–1 hr. Meanwhile, the resistance of junctional insulation rose gradually to a peak, then declined somewhat to a relatively steady level. An upper limit for the steady-level resistivity of junctional membrane was estimated from measurements on partly separated cells coupled by 3–4 strands of 1 μ² cross-section; this estimate is 10⁻² Ω cm², 6 orders of magnitude less than the resistivity of nonjunctional membrane. Viewed in the light of a model proposed earlier (W. R. Loewenstein, 1966), these results suggest that junctional coupling may develop by accretion of diffusion-channel units of ≦10⁻² Ω cm² resistivity.